Editing Reading frame (section)

{{Short description|A specific grouping of the "letters" of a genetic sequence into threes}}<!-- "A" included for clarity: grouping as a result not a process --> 
[[File:Reading Frame.png|thumb|400px|An example of three possible forward reading frames for a strand of DNA.

<div align="center"><span style="color:steelblue;">'''AGG·TGA·CAC·CGC·AAG·CCT·TAT·ATT·AGC'''</span><br />A'''<span style="color:red;">·GGT·GAC·ACC·GCA·AGC·CTT·ATA·TTA</span>'''·GC<br />AG<span style="color:green;">'''·GTG·ACA·CCG·CAA·GCC·TTA·TAT·TAG·'''</span>C</div>]]
In [[molecular biology]], a '''reading frame''' is a specific choice out of the possible ways to read the [[nucleic acid sequence|sequence of nucleotides]] in a [[nucleic acid]] ([[DNA]] or [[RNA]]) molecule as a sequence of triplets. Where these triplets equate to [[amino acid]]s or stop signals during [[Translation (biology)|translation]], they are called [[codon]]s.

A single strand of a [[nucleic acid]] molecule has a [[phosphoryl]] end, called the [[5′-end]], and a [[hydroxyl]] or [[3′-end]]. These define the [[Directionality (molecular biology)|5′→3′ direction]]. There are three reading frames that can be read in this 5′→3′ direction, each beginning from a different nucleotide in a triplet. In a double stranded nucleic acid, an additional three reading frames may be read from the other, [[Complementarity (molecular biology)|complementary]] strand in the 5′→3′ direction along this strand. As the two strands of a double-stranded nucleic acid molecule are antiparallel, the 5′→3′ direction on the second strand corresponds to the 3′→5′ direction along the first strand.<ref>{{cite journal |title=Quantitative sequence and open reading frame analysis based on codon bias |journal=Systemics, Cybernetics and Informatics |volume=4 |issue=1 |pages=65–72 |vauthors=Rainey S, Repka J |url=http://www.iiisci.org/Journal/CV$/sci/pdfs/P842315.pdf }}</ref><ref name=pmid10331277>{{cite journal|title=CRITICA: Coding Region Identification Tool Invoking Comparative Analysis |vauthors=Badger JH, Olsen GJ |journal=Mol Biol Evol |date=April 1999 |volume=16 |issue=4 |pages=512–24 |pmid=10331277 |doi=10.1093/oxfordjournals.molbev.a026133|doi-access=free }}</ref>

In general, at the most, one reading frame in a given section of a nucleic acid, is biologically relevant ([[open reading frame]]). Some viral transcripts can be translated using multiple, overlapping reading frames. There is one known example of overlapping reading frames in mammalian [[mitochondrial DNA]]: coding portions of genes for 2 subunits of ATPase overlap.

[[File:Open reading frame.jpg|thumbnail|right|An example of a section of DNA translated by a computer in all six possible reading frames. The Open Reading Frames (ORFs) for Gene 1 and 2 are highlighted]]